for those running without boost (13.5)...
was able to fit a 100t spur (64p) with a 46t pinion without modifying anything... all i had to do was add 1mm spacers and use slighly longer screws to move the spur out a bit (only because i don't have a 100T RW or Xray spur that has the offset built in already). can still use bigger pinions as there seems to be enough space (maybe up to a 50T)
its just a pain to set as you need to take the whole spurgear assembly in and out to mesh the spur and pinion.
attached some pix.